colored shadows for transparent objects with shadow catcher
I do not believe this is possible at this point with just the shadow catcher function added in v2.79. 

The function is imperfect for compositing, it also does not catch light or refraction/reflections for example. 
Its just a quick way to composite your scene for mock-up purposes.

I would suggest to use the compositor and render passes to achieve the desired effect, which is much more involved and exceeds the answer to this question.